Such actuators are known for dispensing fluids from cartridges. Such known actuators make use of caterpillar movement, but to achieve this, they are constructed to comprise typically three separate active elements. Two elements are necessary for blocking and releasing parts of the actuator and a third element is necessary to move the actuator along its longitudinal direction. Problem of such constructions is the complex structure of an actuator with three different and separate active elements as well as the high costs of such an actuator. First attempts to construct the two elements for blocking and releasing in a passive way led to the disadvantage of bad caterpillar movement. In particular such bad caterpillar movement with respect to the actuation way during one caterpillar cycle is of high disadvantage for the use in medical systems because it could lead to false dosage, in particular underdosage. For example in the use for insulin dispending, such an underdosage could be even life-threatening.